At present, the transmission of channels and contents in the broadcast mode (satellite, cable, terrestrial) is based on the concept of having a playout system which sequentially emits, via a playlist, a series of channels and/or contents. The channels can be sent in SDI (Serial Digital Interface) format or through IP (Internet Protocol) streams over an Ethernet network toward a system of real-time compression, which is typically composed of one or more encoders (for example complying with MPEG2, MPEG4, AVC, H.264 standards) which perform the compression either in a CBR mode (Constant Bit Rate, i.e. parameters and a fixed bit rate are assigned to the components audio, video and channel data) or VBR (Variable Bit Rate). In particular, the VBR process exploits, frame by frame, a statistic to give more bandwidth to the channel (of a group of channels) which has contents requiring more bandwidth in order to have a good quality as compared to other channels in the same frame requiring less bandwidth; in this manner, for example, it is possible to maintain the total bandwidth (for example of a transponder and/or a digital terrestrial Mux) of the different channels of the group fixed.
To date, the management of compression, though optimized by the VBR process, has been based on real-time compression with a latency, i.e. the time difference between the instant at which a frame enters the encoder and the instant at which it is output compressed, which varies from a few milliseconds to a few seconds (for example two seconds).
The encoder thus has only a few available frames to analyze; the compression routines therefore cannot perform accurate analyses of the video, which determines a limit to their ability to reduce (compress) the video stream in terms of the ratio between quality and size of the data flow (bit rate or bandwidth) compared to what can be obtained with encoders that work off-line (for example encoders for VOD, Video On Demand) and which thus have the possibility of analyzing the entire video.
Therefore, the known types of encoding currently applied to linear streams of content require a high transmission bandwidth for the reasons set forth above.